Revision as of 19:24, 22 August 2008

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Problem: it takes a long time (10min+) before the Freerunner gets first GPS data

It was found that the OpenMoko FreeRunner GPS has a long Time To First Fix (TTFF) with the SD card in the phone. This thread indicates that there is interference from the SD card slot, as without the SD card inserted it the TTFF are much shorter.

More specific: the GPS signal level drops by -20dBm, i.e. factor 100. Signal strength of a GPS satellite above your head is around -127dBm. Needed strength for a first fix is -145dBm with a minimum of three satellites. Once the GPS chip has a fix, it can operate at signal levels of -157dBm, thus making it possible to operate while there is data transfer from/to the SD card.

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Problem: it takes a long time (10min+) before the Freerunner gets first GPS data

It was found that the OpenMoko FreeRunner GPS has a long Time To First Fix (TTFF) with the SD card in the phone. This thread indicates that there is interference from the SD card slot, as without the SD card inserted it the TTFF are much shorter.

More specific: the GPS signal level drops by -20dBm, i.e. factor 100. Signal strength of a GPS satellite above your head is around -127dBm. Needed strength for a first fix is -145dBm with a minimum of three satellites. Once the GPS chip has a fix, it can operate at signal levels of -157dBm, thus making it possible to operate while there is data transfer from/to the SD card.